1. Field of the Invention
The present invention relates to lens control technology in an imaging apparatus, such as a camera.
2. Description of the Related Art
In a so-called inner focus type lens system, in which a focus lens unit is disposed on an optical axis behind a zoom lens unit, zooming is generally performed by tracing a locus selected from information about a plurality of loci (electronic cam loci) or information corresponding to the loci illustrated in FIG. 5, stored in memory. Information about a plurality of loci (electronic cam loci) or information corresponding to the loci shown in FIG. 5 may be information indicating the loci themselves or may be functions each having a variable corresponding to a lens position.
When the zoom lens unit is moved from a telephoto end to a wide-angle end, because a plurality of loci converge in a direction from a state that they are separated by some spaces from each other as illustrated in FIG. 5, an in-focus state can be maintained even if zooming is carried out by the above-described locus tracking method. However, when the zoom lens unit is moved from the wide-angle end toward the telephoto end, it is not certain which locus the focus lens unit, which has been at a convergent point, moves along, and the in-focus state cannot be maintained by a similar locus tracking method.
In a control method discussed in Japanese Patent No. 2795439, the movement of the focus lens unit is controlled by switching its direction to forcibly move away from the in-focus position and move in the direction of the in-focus position (the locus tracking speed is changed) when the zoom lens unit is moved (for zooming), by using an AF evaluation value signal (sharpness signal) obtained from high-frequency components of an image signal by a contrast method. In this manner, the tracking locus is corrected.
Moreover, Japanese Patent No. 275439 discusses a method for improving the accuracy of selection (specification) of the tracking locus by changing an increase-decrease cycle in the sharpness signal, which has been made possible by changing the variation of the tracking speed according to an object distance, a focal length, or a depth of field.
Japanese Patent Application Laid-Open No. 2005-234325 discusses an apparatus including an external distance metering unit.
However, information corresponding to a distance to a photographic object may sometimes include errors. This information including errors may increase the possibility of loss of consistency with information corresponding to loci as illustrated in FIG. 5.